What is fertilizer, and why do cannabis plants need it?

Fertilizer provides essential nutrients like nitrogen, phosphorus, and potassium to help cannabis plants grow strong, healthy, and produce high yields. In most grow setups, regular feeding is required to avoid deficiencies and promote optimal growth.

What nutrients are essential for healthy cannabis growth?

Cannabis needs macronutrients like nitrogen, phosphorus, and potassium, plus secondary nutrients like calcium, magnesium, and sulfur. Micronutrients such as iron, zinc, and boron are also vital for plant health and development.

When should I start feeding cannabis plants nutrients?

Start feeding once your cannabis seedlings develop their first true leaves. In coco or hydro, feeding may begin as early as day 7–10. In soil, wait until the plant shows signs of slowed growth or pale lower leaves.

What do NPK values mean on cannabis fertilizer?

NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K), the three primary macronutrients. Ratios like 3-1-2 or 1-4-5 guide what stage of growth the fertilizer supports—veg or bloom.

How do I know if my cannabis plant is overfed or underfed?

Check the EC/PPM of your runoff water. If it's much higher than your input, nutrients are building up—overfeeding. If it's much lower, your plant may be hungry—underfeeding.

Does this calculator work for LED, HID, or CMH lights?

Yes — it works for all light types. Efficiency may vary, but wattage is a great starting point for estimating needs.

How accurate is this wattage estimate?

It provides a solid estimate based on grow area and stage. For precision, measure PPFD directly at the canopy.

What if I use multiple lights?

Just add up the total wattage of all your lights. This tool helps you see if you're within the optimal range.

Wattage Calculator

Grow Light Wattage Calculator

Light. Data. Growth. Smarter cultivation starts here.

Grow Light Wattage Calculator

Find out how many watts you need based on your grow space and plant stage.

Grow Area Length (ft) [?] Grow Area Width (ft) [?] Plant Stage:

Light Hours per Day [?] Select Your State (optional):Electricity Rate ($/kWh):

Grow Journal

Plan, track, and reflect on your grow. The Grow Journal helps you organize tools, notes, schedules, and specs — all in one place.

Learn About the Grow Journal Open Dashboard

How does this work?

We estimate watts needed based on area size and plant stage:

Veg: 20–30 watts per sq ft
Flower: 30–50 watts per sq ft

Example: a 4×4 grow (16 sq ft) in flower needs ~480–800 watts.

Tool by GrōHaus — helping growers dial in their light, space, and yield.

Wattage Calculator

Grow Light Wattage Calculator

Grow Journal

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